Method for the termination of living polymers, and compounds suitable for the purpose

ABSTRACT

Coupling agents of general formula ##STR1## and their use in a method for the termination of living polymers obtained by anionic polymerization of diene and/or vinylaromatic monomers.

This is a divisional of application Ser. No. 602,213 filed Apr. 19,1984, now U.S. Pat. No. 4,618,449.

If effected under suitable conditions and with suitable monomers (M.SZWARC Carbanions, Living Polymers and El. Transfer Processes,Interscience Publishers, J. Wiley & Sons, New York 1968), anionicpolymerisation enables living polymers to be obtained which are wellsuitable for appropriate transformations. Among these, the couplingreaction (coupling of two or more polymer segments by a coupling agentto give a polymer having a molecular weight of nPM, where PM is themolecular weight of the polymer segment and n the functionality of thecoupling agent) is certainly one of the most investigated, in that by asimple approach it enables important variations to be obtained, even interms of the properties of the treated polymers. For example, in thepolymerisation of dienes it is possible in this manner to increase theMooney viscosity, decrease the cold flow, increase the green tensilestrength and modify the molecular weight distribution at will.

In the synthesis of block polymers constituted by linear or branchedconjunctions of elements A and B (where A is a polyvinyl and/orpolyisopropanyl aromatic sequence and B is a diene sequence, which canalso be hydrogenated), the use of efficient coupling agents is a factorof essential importance in that it is a known fact that the possiblepresence of the unreacted substances A and B in the final productdepresses the technological properties thereof. Numerous examples ofcoupling agents are reported in the literature [H. L. HSIEH, RubberChem. and Techn. 49 (5), 1305 (1976)]. We have now found that polystyrylderivatives, as exemplified hereinafter, can be conveniently used as newcoupling agents in that in addition to possessing the typical propertiesof the best coupling agents described in the literature (see H. L.Hsieh, ibid) they have the following advantages:

(i) the coupling reaction can also be effected without the use ofactivators

(ii) the coupling reaction can be effected at a lower temperature thanthat usually used for conventional coupling agents, for equal reactiontimes

(iii) by-products are not formed as the coupling reaction is a reactionof addition rather than elimination.

The products which we have found to be efficient coupling agents arethose of the following general formula ##STR2## where X is an organicradical of the following structures, or a multivalent derivativethereof: ##STR3##

n is a whole number between 2 and 6 and preferably 2, 3 or 4; R can behydrogen, an alkyl radical which preferably has a tertiary carbon atomdirectly attached to the aromatic ring, or a cycloalkyl, alkoxy,dialkylamino or aromatic radical.

R contains between 0 and 18 C atoms.

Said coupling agents are prepared in a simple manner and with highyields by the method of A. E. Siegrist and colleagues, [HelveticaChimica Acta 52 (8), 2521 (1969), ibid 63 (5), 1311 (1980)] starting forexample from the methyl derivatives of the structures exemplifiedheretofore by X: ##STR4##

Typical non-limiting examples of methyl compounds used are:2,6-dimethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine,2,3-dimethylnaphthalene, 1,5-dimethylnaphthalene,2,3,6-trimethylnaphthalene, 1,3-dimethylbenzene, 1,3,5-trimethylbenzene,p-ditolylether, 4,4'-dimethyldiphenylethyne.

The compounds according to the present invention can be used inprocesses for the polymerisation of monomers susceptible to anionicinitiation under living conditions, and in particular for thepolymerisation of diene and/or vinylaromatic monomers.

The conjugated dienes used contain between 4 and 12 carbon atoms, andpreferably between 4 and 8.

Said monomers comprise: 1,3-butadiene, isoprene, 2,3-dimethylbutadiene,piperylene, 3-butyl-1,3-octadiene and 2-phenyl-1,3-butadiene. Thevinylaromatic monomers contain between 8 and 20 carbon atoms, andpreferably between 8 and 14. Typical examples are: styrene,α-methylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene,2-isopropanylnaphthalene, p-phenylstyrene, 3-methylstyrene,α-methyl-p-methylstyrene and p-cyclohexylstyrene.

The conjugated dienes and/or vinylaromatic monomers can be polymerisedalone, in mixture, or sequentially to form homopolymers, statisticalcopolymers or block copolymers.

The polymerisation is effected in solution at a temperature of between-100° and +200° C. and preferably between 0° and 110° C., and at apressure which is that of the system under the temperature conditionsused, but higher or lower pressures are non contra-indicated.

Suitable solvents include paraffin, cycloparaffin and aromatichydrocarbons. Typical examples are cyclohexanol, hexane, pentane,heptane, isooctane, benzene, toluene and mixtures thereof. Smallquantities of polar compounds can be added in known manner to thesolvent in order to obtain a 1,2 configuration in diene polymerisation,or in order to increase the efficiency of the initiator in thepolymerisation of vinylaromatic monomers.

The initiators are the typical anionic initiators used for this purpose.

Organometal compounds of formula R-Me are preferably used, where R is analiphatic, cycloaliphatic or aromatic hydrocarbon radical, and Me is analkaline metal, preferably lithium.

The quantity of initiator used is relative to the molecular weight ofthe polymer to be obtained. The polymerisation is conducted underconditions such as to ensure the living state of the polymer obtained(M. SZWARC Carbanions, Living Polymers and El. Transfer Processes,Interscience Publishers, J. Wiley & Sons, New York 1968).

The coupling agent can be introduced into the reaction environment inany manner, either by a single addition of by partial additions, at therequired time.

It is preferably introduced in the required quantity on termination ofthe polymerisation.

The molar quantity of coupling agent (m_(AC)) to be added is given bythe formula

    m.sub.AC =m.sub.CA /f.sub.AC

where

m_(CA) is the moles of active centres in the living polymer

f_(AC) is the functionality of the coupling agent.

The amount of coupling agent used influences the coupling yield.Obviously a stoichiometric ratio of the polymer active centre to thecoupling agent active centre (taking its functionality into account)favours maximum yield.

The temperature at which the coupling reaction is carried out depends onthe type of agent used, the type of polymer undergoing reaction, andother factors such as the reaction medium. Generally it can vary between20° and 150° C., but is preferably between 40° and 80° C. The contacttime is between some minutes and some hours, preferably being between 10minutes and 2 hours.

Sometimes polar activators can be used to increase the coupling rate. Inthe case of the more active coupling compounds claimed herein, the useof these activators is not required.

The solvents are those used in polymerisation.

The coupling reaction is conducted at the natural pressure of the systemat the operating temperature, but higher or lower pressures are notcontra-indicated.

EXAMPLE 1

The polymerisation and coupling are carried out in a 1 liter reactorfitted with an agitator, pressure indicator, thermocouple well and apassage for introducing the reagents and inert gas.

500 cm³ of anhydrous cyclohexane, 12 g of styrene and 1.0 mmoles ofLi-sec.butyl are fed in that order, and are allowed to polymerise at 60°C. for about 1 hour. After this time, 30 g of butadiene are added andthe polymerisation is completed at 60° C. within 1 hour. A very smallquantity of this polymer is withdrawn and fed to the various analyses.0.45 mmoles of a solution of 2,6-distyrylpyridine in benzene-cyclohexane(50--50 v/v) are then injected at 60° C. After 15 minutes the polymer,to which 1 g of antioxidant is added, is coagulated with an excess ofmethanol to obtain 42 g of product, which is dried at 60° C. for 15hours under vacuum.

The properties of the polymers before and after the coupling reactionare given in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Composition.sup.(a)                                                                        Molecular.sup.(b)   Coupling.sup.(4)                             % weight     weight, g/mole                                                                        Polydispersity.sup.(c)                                                                Gel efficiency                                   Sample                                                                             STY BUT ----Mw                                                                            ----Mn                                                                            index   %   %                                            __________________________________________________________________________    A-B  30  70   55000                                                                            50000                                                                             1.1     0   --                                           A-B-A                                                                              30  70  127000                                                                            98000                                                                             1.3     0   >90                                          __________________________________________________________________________     NOTES:                                                                        .sup.(a) by N.M.R.                                                            .sup.(b) by G.P.C. measurements in accordance with the procedure describe     by L. H. Tung, J. Appl. Polym. Sci. 24, 953 (1979)                            .sup.(c) as the ratio of ----Mw/----Mn                                        .sup.(d) as the ratio of the area of the polymer peak after the coupling      reaction (AB-A) to the area of the polymer peak before the coupling           reaction (AB), these areas being determined by G.P.C.                    

The polymer A-B-A of Example 1 has the following technologicalproperties:

elongation: 915%

ultimate tensile stress: 32 MPa

whereas the corresponding polymer A-B shows an ultimate tensile stressof about 3 MPa for equal elongation.

If the 2,6-distyrylpyridine is replaced by dichlorodiphenylsilane as thecoupling agent, then under the same experimental conditions the couplingefficiency is less than 10%.

EXAMPLE 2

Example 1 is repeated, but using 2,4,6-tristyrylpyridine (0.30 mmoles),and polymers (A-B and A-B-A) are isolated having the properties given inTable 2.

                                      TABLE 2                                     __________________________________________________________________________    Composition.sup.(a)                                                                        Molecular.sup.(b)   Coupling.sup.(4)                             % weight     weight, g/mole                                                                        Polydispersity.sup.(c)                                                                Gel efficiency                                   Sample                                                                             STY BUT ----Mw                                                                            ----Mn                                                                            index   %   %                                            __________________________________________________________________________    A-B  30  70   57000                                                                             52000                                                                            1.1     0   --                                           A-B-A                                                                              30  70  196000                                                                            145000                                                                            1.35    0   about 95                                     __________________________________________________________________________     Notes: see Table 1                                                       

EXAMPLE 3

50 g of α-methylstyrene and 1 mmole of Li-sec.butyl are fed into thereactor described in Example 1, and polymerised at 20° C. for 1 hour and15 minutes. At the end of this time, 5 g of butadiene are added andallowed to interact for 15 minutes, after which 500 cm³ of cyclohexaneand 25 g of butadiene are added, allowing polymerisation to continue at60° C. for 1 hour. A small sample is withdrawn, and 0.45 mmoles of2,6-distyrylpyridine are then injected, the coupling reaction beingconducted at a temperature of 60° C. for 15 minutes. A polymer isisolated in the usual manner (43 g) and has the properties shown inTable 3, which also gives the properties of the product A-B.

                                      TABLE 3                                     __________________________________________________________________________    Composition.sup.(a)                                                                        Molecular.sup.(b)   Coupling.sup.(4)                             % weight     weight, g/mole                                                                        Polydispersity.sup.(c)                                                                Gel efficiency                                   Sample                                                                             αSTY                                                                        BUT ----Mw                                                                            ----Mn                                                                            index   %   %                                            __________________________________________________________________________    A-B  30  70   63000                                                                            55000                                                                             1.15    0   --                                           A-B-A                                                                              30  70  139000                                                                            99000                                                                             1.40    0   about 90                                     __________________________________________________________________________     Notes: see Table 1                                                       

EXAMPLE 4

Example 1 is repeated but using 2,3-distyrylnaphthalene as the couplingagent. The relative data are given in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Composition.sup.(a)                                                                        Molecular.sup.(b)   Coupling.sup.(4)                             % weight     weight, g/mole                                                                        Polydispersity.sup.(c)                                                                Gel efficiency                                   Sample                                                                             STY BUT ----Mw                                                                            ----Mn                                                                            index   %   %                                            __________________________________________________________________________    A-B  30  70   53900                                                                            49000                                                                             1.1     0   --                                           A-B-A                                                                              30  70  128000                                                                            95000                                                                             1.35    0   about 85                                     __________________________________________________________________________     Notes: see Table 1                                                       

EXAMPLE 5

The polymerisation test described in Example 3 is repeated, but using1,3,5-tristyrylbenzene as the coupling agent. The data relative to theisolated polymers are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________    Composition.sup.(a)                                                                        Molecular.sup.(b)   Coupling.sup.(4)                             % weight     weight, g/mole                                                                        Polydispersity.sup.(c)                                                                Gel efficiency                                   Sample                                                                             αSTY                                                                        BUT ----Mw                                                                            ----Mn                                                                            index   %   %                                            __________________________________________________________________________    A-B  29  71   50600                                                                             46000                                                                            1.1     0   --                                           A-B-A                                                                              29  71  186000                                                                            133000                                                                            1.4     0   >90                                          __________________________________________________________________________     Notes: see Table 1                                                       

EXAMPLE 6

Example 1 is repeated, but polymerising isoprene instead of butadiene.2,6-distyrylpyridine is used as the coupling agent, the reaction beingconducted at 90° C. for 30 minutes.

The data relative to the isolated polymer (about 42 g) and thecorresponding product A-B are given in Table 6.

                                      TABLE 6                                     __________________________________________________________________________    Composition.sup.(a)                                                                        Molecular.sup.(b)   Coupling.sup.(4)                             % weight     weight, g/mole                                                                        Polydispersity.sup.(c)                                                                Gel efficiency                                   Sample                                                                             STY BUT ----Mw                                                                            ----Mn                                                                            index   %   %                                            __________________________________________________________________________    A-B  30  70   52800                                                                            48000                                                                             1.1     0   --                                           A-B-A                                                                              30  70  124000                                                                            92000                                                                             1.35    0   about 80                                     __________________________________________________________________________     Notes: see Table 1                                                       

EXAMPLE 7

About 40 g of butadiene are polymerised with 1 mmole of Li-sec.butyl isabout 400 cm³ of cyclohexane for about 1 hour at 60° C., in theapparatus heretofore described. At the end of this time, a mixture of2,6-distyrylpyridine (0.225 mmoles) and 2,4,6-tristyrylpyridine (0.5mmoles) is added, and the reaction allowed to proceed for 15 minutes at60° C. The G.P.C. diagram of the isolated polymer shows the presence ofpeaks of products with a different degree of coupling and with a widermolecular weight distribution than that of the polymer A-B.

What is claimed is:
 1. A method for the termination of livingmacroanions obtained by anionic polymerisation of diene and/orvinylaromatic monomers, consisting of introducing into thepolymerisation mixture a coupling agent of the general formula: ##STR5##where X is an organic radical of valency n selected from the followingchemical structures: ##STR6## n is a whole number from 2 to 6,inclusive, and R is hydrogen or an alkyl, cycloalkyl, alkoxy,dialkylamino or aromatic radical containing 1 to 18 carbon atoms, andwhere the molar quantity of said coupling agent added is calculatedaccording to the formula m_(AC) =m_(CA) /f_(AC), where m_(CA) is themolar quantity of active centers in the living macroanion, f_(AC) isequal to n, and m_(AC) is equal to the molar quantity of said couplingagent added.
 2. A method as defined in claim 1, wherein the method iscarried out in the absence of polar activators.
 3. A method as definedin claim 1, wherein said method is carried out at a temperature of20°-150° C.
 4. A method as defined in claim 1, wherein said method iscarried out at a temperature of 40°-80° C.
 5. A method for thetermination of living macroanions obtained by anionic polymerisation ofdiene and/or vinylaromatic monomers, consisting of introducing into thepolymersation mixture a coupling agent of general formula ##STR7## wheren is a whole number from 2 to 6, inclusive, and R is hydrogen or analkyl, cycloalkyl, alkoxy, dialkylamino or aromatic radical and containsfrom 1 to 18 carbon atoms.
 6. A method a defined in claim 5, wherein nis 2, 3 or
 4. 7. A method as defined in claim 6, wherein R is hydrogen.8. A method as defined in claim 5, wherein said coupling agent is2,6-distyrylpyridine.
 9. A method as defined in claim 5, wherein saidcoupling agent is a mixture of 2,6-distyrylpyridine and2,4,6-tristyrylpyridine.